1. Field of The Invention
This invention relates to an electron gun assembly for cathode ray tubes and method of assembling the same, and more particularly to an electron gun assembly having direct heated cathodes.
2. Brief Description of The Prior Art
Recently, low power consumption property is desired for a cathode ray tube of a TV receiver. To reduce the power consumption, it is planned to lower the deflection power or the cathode heating power of the cathode ray tube.
Especially in a color cathode ray tube having a three-electron-gun assembly, the neck portion of the tube, in which the electron gun assembly is installed, must be thin to reduce deflection power. Consequently the thickness of the gun assembly becomes small and the spaces between respective guns become narrow. The three electron gun assembly is composed of a first grid electrode, a second grid electrode, a third grid electrode, a fourth grid electrode and three cathodes, all of which are secured by glass rods with predetermined distances to each other. Such a narrow three-electron-gun assembly is what is called a unitized gun. Therefore, corresponding electrodes of three electron gun units are equipotential. Accordingly, input signals to the three electron guns are applied to respective cathodes. Consequently, the spacing between the cathode and the first grid electrode in each gun unit must be accurate.
One example of a direct heated cathode used for electron guns of a color cathode ray tube is shown in FIG. 1A and 1B. Reference numeral 1' denotes a plate-like insulative support member made of ceramics and having an aperture 2 at the center portion thereof. At the periphery of the aperture 2' is integrally formed an annular convexity. Three heaters 5 are stretched on the annular convexity equally apart from each other. At the center of each heater 5 is secured an electron emitting member 7'. Both ends of the heater 5' are supported by two resilient ribbons 8' secured to a lead terminals 6' fixed to the support member 1'. These constitute three direct heated cathodes. Furthermore the direct heated cathodes are combined with a plurality of grid electrodes (not shown) with glass rods to construct a three-electron-gun assembly.
It is difficult to set the distances between the cathode and the respective electrodes when these electrodes are assembled. Particularly in an electron gun in which three input signals are applied to three cathodes respectively, the spacing between the electron emitting member and the first grid must be exactly adjusted to the predetermined value in each gun unit. However, conventional gun structure is hard to adjust exactly the spacing.